NAME¶
snmp_sess_init, snmp_sess_open, snmp_sess_session, snmp_sess_send,
snmp_sess_async_send, snmp_sess_select_info, snmp_sess_read,
snmp_sess_timeout, snmp_sess_synch_response, snmp_sess_close, snmp_sess_error
- session functions
SYNOPSIS¶
#include <net-snmp/session_api.h>
void snmp_sess_init(struct snmp_session *session);
void *snmp_sess_open(struct snmp_session *session);
struct snmp_session *snmp_sess_session(void *handle);
int snmp_sess_send(void *handle, struct snmp_pdu
*pdu);
int snmp_sess_async_send(void *handle,
struct snmp_pdu *pdu,
snmp_callback callback,
void *callbackData);
int snmp_sess_select_info(void *handle,
int *numfds, fd_set *fdset,
struct timeval *timeout,
int *block);
int snmp_sess_read(void *handle, fd_set
*fdset);
void snmp_sess_timeout(void *handle);
int snmp_sess_synch_response ( void *handle,
netsnmp_pdu *pdu,
netsnmp_pdu **response);
int snmp_sess_close(void *handle);
void snmp_sess_error(void *handle, int *pcliberr,
int *psnmperr, char **pperrstring);
DESCRIPTION¶
These functions define a subset of the API that can be used to manage single
SNMP sessions in a multi-threaded application. Except for
snmp_sess_session(), these functions are single session versions of the
traditional SNMP library API.
Note that these functions use an opaque pointer (
handle in the above
prototypes) to identify a single session in lieu of a
session pointer
(as in the traditional API).
snmp_sess_init() prepares a struct snmp_session that sources transport
characteristics and common information that will be used for a set of SNMP
transactions. After this structure is passed to
snmp_sess_open() to
create an SNMP session, the structure is no longer used. Instead the opaque
pointer returned by
snmp_sess_open() is used to refer to that session
henceforth.
SNMP sessions that are created with
snmp_sess_open() are not affected by,
and SHOULD NOT BE USED WITH,
snmp_select_info(),
snmp_read(),
snmp_timeout() nor
snmp_close(). Rather the equivalent single
session functions described here should be used.
snmp_sess_init() and
snmp_sess_open() each take as input a pointer
to a struct snmp_session object. This structure contains information for a set
of transactions that will share similar transport characteristics.
snmp_sess_session() takes the opaque session handle and returns a
pointer to its associated struct snmp_session.
snmp_sess_send() and
snmp_sess_async_send() each take a
pdu
parameter, which points to a struct snmp_pdu object containing information
that describes a transaction that will be performed over an open session.
Consult snmp_api.h for the definitions of these structures.
With the
snmp_sess_async_send() call,
snmp_sess_read will invoke
the specified callback when the response is received.
snmp_sess_select_info(),
snmp_sess_read() and
snmp_sess_timeout() provide an interface for the use of the
select(2) system call so that SNMP transactions for a single session
can occur asynchronously.
snmp_sess_select_info() is passed the information that would have been
passed to
select(2) in the absence of SNMP. For example, this might
include file descriptors associated with the main loop of a graphical
application. This information is modified so that SNMP will get the service it
requires from the call to
select(2). In this case,
numfds,
fdset and
timeout correspond to the
nfds,
readfds
and
timeout arguments to
select(2) respectively. The only
exception is that timeout must ALWAYS point to an allocated (but perhaps
uninitialized)
struct timeval (it cannot be NULL as for
select(2)). If
timeout would have been passed as NULL,
block is instead set to true, and
timeout is treated as
undefined. This same rule applies upon return from
snmp_select_info().
After calling
snmp_sess_select_info() , select(2) should be called
with the returned data. When it returns,
snmp_sess_read() should then
be called with the
fd_set returned from
select(2). This will
read any input from this session's SNMP socket. If
select(2) times out
(that is, it returns zero),
snmp_sess_timeout() should be called to see
if a timeout has occurred on the SNMP session.
snmp_sess_synch_response is a convenience routine that will send the
request, wait for the response and process it before returning. See the
descriptions of
snmp_sess_send , snmp_sess_read etc for details.
DIAGNOSTICS¶
Error return status from
snmp_sess_open() is indicated by return of a
NULL pointer. Error return status from
snmp_sess_close() and
snmp_sess_send() is indicated by a return value of 0. A successful
status will return 1.
Further information can be obtained by using
snmp_sess_error() to see
what type of error has occurred. This function returns the SNMP
snmp_errno variable, the value of the system
errno variable, and
a string interpretation of both variables. The string must be freed after use
by the caller.
For errors returned by
snmp_sess_open(), use the corresponding function
snmp_error() instead of
snmp_sess_error().
Consult snmp_api.h for the complete set of SNMP library error values. The SNMP
library error value
snmperr can be one of the following values:
- SNMPERR_GENERR
- A generic error occurred.
- SNMPERR_BAD_LOCPORT
- The local port was bad because it had already been allocated or permission
was denied.
- SNMPERR_BAD_ADDRESS
- The host name or address given was not useable.
- SNMPERR_BAD_SESSION
- The specified session was not open.
- SNMPERR_TOO_LONG
- SNMPERR_NO_SOCKET
- SNMPERR_V2_IN_V1
- SNMPERR_V1_IN_V2
- SNMPERR_BAD_REPEATERS
- SNMPERR_BAD_REPETITIONS
- SNMPERR_BAD_ASN1_BUILD
- SNMPERR_BAD_SENDTO
- SNMPERR_BAD_RCVFROM
- SNMPERR_BAD_PARSE
- SNMPERR_BAD_VERSION
- SNMPERR_BAD_COMMUNITY
- SNMPERR_NOAUTH_DESPRIV
- SNMPERR_ABORT
- SNMPERR_UNKNOWN_PDU
- SNMPERR_TIMEOUT
SEE ALSO¶
select(2),
snmp_api(3),
snmp_api.h